Some new designs of mobile communication devices—such as smart phones, tablet computers, and laptop computers—contain one or more Subscriber Identity Module (“SIM”) cards that provide users with access to multiple separate mobile telephony networks. Examples of mobile telephony networks include GSM, LTE, TD-SCDMA, CDMA2000, and WCDMA. A mobile communication device that includes one or more SIMs and connects to two or more separate mobile telephony networks using one or more shared radio frequency (“RF”) resources/radios is termed a “multi-standby” communication device. An example is a dual-SIM-dual-standby (“DSDS”) communication device, which includes two SIM cards/subscriptions that are each associated with a separate radio access technology (“RAT”), and the separate RATs share one RF chain to communicate with two separate mobile telephony networks on behalf of their respective subscriptions. Another example is a single-radio LTE (“SRLTE”) communication device, which includes one SIM card/subscription associated with two RATs that share a single shared RF resource to connect to two separate mobile networks on behalf of the one subscription.
A plurality of RATs on a multi-standby communication device utilize one or more shared RF resources to communicate with their respective mobile telephony networks, and only one RAT may use each RF resource to communicate with its mobile network at a time. Thus, even when a RAT is in an “idle-standby” mode, meaning the RAT is not actively communicating with the network, the RAT may still need to periodically receive access to a shared RF resource in order to perform various network operations. For example, an idle RAT may need the shared RF resource at regular intervals to perform idle-mode operations to receive network paging messages in order to remain connected to the network, etc. on behalf of the RAT's subscription. Therefore, at certain times, the multiple RATs sharing an RF resource may need to use the RF resource to communicate with their respective mobile networks simultaneously.
In conventional multi-standby communication devices, the RAT actively using an RF resource that is shared with an idle RAT may occasionally be forced to interrupt the active RAT's RF operations so that the idle RAT may use the shared RF resource to perform the idle RAT's idle-standby mode operations (e.g., paging monitoring, cell reselection, system information monitoring, etc.). This process of switching access of the shared RF resource from the active RAT to the idle RAT is sometimes referred to as a “tune-away,” as the RF resource must tune away from the active RAT's frequency band or channel and tune to the idle RAT's frequency bands or channels. After the idle RAT has finished its network communications (sometimes collectively referred to herein as “tune-away operations), access to the RF resource may switch from the idle RAT to the active RAT via a “tune-back” operation.
As a result of the multi-standby communication device's tune aways, the signals received by the active RAT may become corrupted and difficult or impossible to decode because portions of the signal, data, packets, etc. sent from the active RAT's network are lost during the tune-away event. As such, tune-away events present a design and operational challenge for shared-radio devices, such as multi-standby communication devices, due to the necessity of tuning away from an active RAT to an idle RAT for the benefit of an inactive RAT in these devices.